The invention pertains to methods of forming dielectric materials, and methods of forming capacitors. The invention also pertains to capacitor constructions.
It is frequently desired to form dielectric materials during semiconductor device fabrication. For instance, capacitor constructions comprise dielectric material separating a pair of capacitor electrodes. Suitable dielectric materials for capacitor constructions include silicon dioxide and silicon nitride, with an exemplary dielectric material comprising a stack of silicon nitride between a pair of silicon dioxide layers.
An advantage of utilizing silicon nitride in capacitor constructions is that it has a higher dielectric constant than silicon dioxide. However, a difficulty in utilizing silicon nitride can occur in attempting to get a uniform coating of silicon nitride over a capacitor electrode. For instance, a capacitor electrode can comprise conductively-doped rugged silicon (for example, conductively-doped hemispherical grain polysilicon). Such rugged silicon has a rough surface texture, and is utilized because the rough surface texture enables more conductive surface area to be provided over a particular footprint than would be provided with a smooth-surfaced structure. A difficulty can occur in attempting to form silicon nitride over the roughened surface structure of rugged silicon. Specifically, silicon nitride is typically provided by chemical-vapor deposition (such as, for example, low pressure chemical vapor deposition utilizing silane and ammonia as precursors), and the nitride deposits non-conformally on the roughed surface of the rugged silicon. Accordingly, if the nitride is provided as a thin layer (less than 100 xc3x85 thick), there can be pinholes extending into the nitride, and even extending through the nitride to expose portions of the underlying rugged silicon surface.
Among the methods which have been developed to compensate for the pinhole problems are methods in which silicon dioxide is formed over the layer of silicon nitride to either fill the pinholes or at least cover the pinholes with a dielectric material. The silicon dioxide can be formed by either chemical vapor deposition, or by oxidation of the silicon nitride surface.
Another method for compensating for pinhole problems is to form silicon dioxide over the rugged polysilicon prior to formation of the silicon nitride. Accordingly, a dielectric material will be beneath the silicon nitride, and any pinholes extending through the silicon nitride can be prevented from exposing the underlying conductive substrate by the intervening layer of silicon dioxide.
In typical prior art processing, both of the above-discussed silicon dioxide methodologies are utilized. In other words, a layer of silicon dioxide is formed before forming the layer of silicon nitride, and a second layer of silicon dioxide is formed after forming the layer of silicon nitride.
It would be desirable to develop methods wherein some or all of the above-discussed difficulties associated with formation of silicon nitride could be eliminated, and particularly it would be desirable to develop methods wherein one or both of the above-discussed layers of silicon dioxide could be eliminated from capacitor constructions.
In one aspect, the invention encompasses a method of forming a dielectric material. A nitrogen-comprising layer is formed on at least some of the surface of a rugged polysilicon substrate to form a first portion of a dielectric material. After the nitrogen-comprising layer is formed, at least some of the substrate is subjected to dry oxidation with one or both of NO and N2O to form a second portion of the dielectric material.
In another aspect, the invention encompasses a method of forming a capacitor. A layer of rugged silicon is formed over a substrate, and a nitrogen-comprising layer is formed on the layer of rugged silicon. Some of the rugged silicon is exposed through the nitrogen-comprising layer. After the nitrogen-comprising layer is formed, at least some of the exposed rugged silicon is subjected to dry oxidation conditions with one or both of NO and N2O. Subsequently, a conductive material layer is formed over the nitrogen-comprising layer.
In yet another aspect, the invention encompasses a capacitor structure. The structure includes a first capacitor electrode comprising a rugged polysilicon layer, a nitrogen-comprising layer on the rugged polysilicon layer, and a second capacitor electrode. The nitrogen-comprising layer is between the first and second capacitor electrodes.